1. Field of the Invention
The invention is generally related to the inspection of nuclear fuel rods and in particular to a drive unit for driving and rotating a fuel rod in a test tank for ultrasonic inspection of the end closure weld.
2. General Background
During fabrication of nuclear fuel rods, ultrasonic (UT) inspection is performed on all fuel rod closure welds. The end of the fuel rod to be inspected is inserted horizontally through a seal into a test tank filled with water. The inspection is performed by rotating the fuel rod about its longitudinal axis and scanning the weld with the UT transducer during rotation.
Equipment commonly used in such inspections utilizes a push/pull unit located at the end of the fuel rod away from the test tank and a rotation unit located adjacent to the test tank to position and manipulate the fuel rod for the UT inspection. The carriage mounted push/pull unit travels on linear ball bushings to insert the fuel rod in the test tank and incorporates an air cylinder operated clamp to withdraw the fuel rod at the completion of the inspection cycle. Rotation of the fuel rod is provided by a 3-jaw lathe chuck which is turned by an electric motor through a timing belt drive. An electrically operated actuator opens and closes the chuck jaws. The push/pull unit pushes the leading end of the fuel rod through the electric actuator and chuck into the test tank against a retractable stop. The actuator then closes the chuck to grip the fuel rod and the motor rotates the chuck and fuel rod for the UT inspection cycle. Upon completion of the test cycle, the motor is shut off and the actuator opens the chuck jaws to release the fuel rod. The fuel rod is then drawn back from the test tank and through the chuck and actuator by the push/pull unit. During the return stroke, and after the fuel rod has cleared the chuck and actuator, the clamp on the push/pull unit opens to release the fuel rod which is left on the handling rack for transfer to the next station.
One problem presented by such equipment is the requirement of frequent maintenance due to water on the fuel rod being left on the internals of the chuck and actuator during withdrawal of the fuel rod from the test tank. Particularly after periods of disuse, rusting can cause these parts to seize, requiring disassembly and rebuilding. Another problem is that the clamping action of the 3-jaw chuck on the fuel rod causes axial displacement of the fuel rod in excess of the 0.001 inch tolerance necessary for the new seal welds. The clamping action of the 3-jaw chuck also increases the potential for damage to the fuel rod itself in the form of the fuel rod cladding being scratched and removed from the exterior of the rod or the relatively thin wall of the fuel rod being dented. The metallic cladding is important in retaining fission gas products within the fuel rod and protecting the fuel rod from the corrosive environment while dents in the fuel rod wall may limit movement of fuel pellets in the rod as they tend to change shape due to irradiation during their operational life span.
Inspection devices which applicant is aware of include the following.
U.S. Pat. No. 4,368,644 entitled "Tool For Inspecting Defects In Irregular Weld Bodies" discloses a tool which is actuated to move an ultrasonic inspection transducer over the surface of an irregular weld body such as the intersection of the nozzle of a reactor vessel to the vessel.
U.S. Pat. No. 4,660,419 entitled "Reference Standard For Calibration Of Ultrasonic Arrays" discloses the use of an array of ultrasonic transducers disposed along a circular arc for examining tubular objects moving therethrough and a calibrating cylinder having calibrating flaws therein.
U.S. Pat. No. 4,681,730 entitled "Process And Device For Detecting Leaking Nuclear Fuel Elements In A Nuclear Assembly" discloses the use of an ultrasonic transducer carried by rod means for insertion in the assembly between an end piece and the caps of the element.
U.S. Pat. No. 4,096,757 entitled "Method And Apparatus For Examining Weld Defects In Vertical Pipes By Supersonic Waves" discloses a supersonic probe on a rotary shaft revolved along the inner surface of a pipe to be examined.
U.S. Pat. No. 4,686,078 entitled "Method And Apparatus For Displacing A Reactor Weld Scanner Assembly By Variable Buoyancy" discloses the use of buoyancy chambers to move a scanner and telescopic boom into position relative to a reactor vessel.
It is seen that the known art does not address the above problems of axial displacement tolerance and water deposition on the drive unit.